The present invention relates generally to a method and apparatus for curing resin-coated particles of sand and, more particularly, to a method and apparatus for forming a proppant comprising sand grains which are individually coated with a cured thermoset resin.
Resin-coated silica sand particles have well known uses as shell molds and cores in the foundry art. One process of preparing phenolformaldehyde resin-coated shell sand is described in U.S. Pat. No. 4,090,995 to Smillie. These resin-coated sand particles are cured when they are formed into shell molds and cores. Recently it has been discovered that pre-cured resin-coated sand particles (particularly phenolformaldehyde resin-coated) have great utility as a propping agent in oil wells, gas wells, water wells and other similar boreholes. Previously, uncured resin-coated sand has been introduced into boreholes for use as a proppant; for example, U.S. Pat. No. 3,929,191 to Graham et al. describes a proppant which is cured in the borehole by borehole temperature and pressure. When properly cured, resin-coated silica sand particles cured before being introduced into the borehole have been shown to give good performance as a propping agent up to about 10,000 p.s.i. In particular, sand particles coated with cured phenolformaldehyde resin have proven particularly useful.